text:
Who invented the cabin chime? What aircraft was the first to use it?
While looking for one to set as my ringtone, I became interested in the history of the cabin chime - the "bing-bong" noise heard on practically every commercial airliner today. I've found tons of downloads for the sound itself and a few posts by pilots and cabin crew on what different chimes or sequences of chimes mean, but nothing on its origin. Anyone?

I just happened to read this a few minutes ago from a flight attendant's blog: "The only thing you have to fear is "the triple high-low chime." That's the captain telling the flight attendants to prepare for an emergency."

Huh. It varies by airline - United, Continental, and another airline use 5 for emergencies, but Delta uses 3 or 5 for normal landings, and Northwest and another one used 4 for "brace for impact."

Related

I can't definitively identify the true origin of the chimes; but the earliest reference to them I can find is in:

ARINC Characteristic 715-3 Airborne Passenger Address Amplifier (PA AMP)
This standard describes the characteristics of a PA AMP designed for
installation in commercial aircraft. Its function is to amplify control voice,  music and internally generated chime audio signals to drive the aircraft cabin  loudspeaker system.

The original ARINC 715 was published in 1978.
The standard they defined is in section 3.4 of the document:

3.4 Chimes
The PA Amplifier equipment should include a chime generator capable of
providing two tones in the four remote controlled sequences that may
be deployed through either the auxiliary or main amplifier utilizing
aircraft strapping. Internal controls shall be provided to adjust the
individual tone levels for balancing the related outputs.
3.4.1 Tone Frequencies
The high tone should be 587 Hz (musical Note D) and the low tone
should be 494 Hz (Musical Note B) signals of a pleasant sounding
musical nature.
3.4.2 Tone Harmonics
The chime tone harmonics should be minimized with the second harmonic
level at least 30 dB below that of the fundamental and each succeeding
harmonic should be a further 3 dB below the preceding harmonic.
3.4.3 Tone Decay
The single high and low tone levels should decay to a level 30 ±6 dB
below the peak level within 900 milliseconds from the peak. The second
tone of the high/low combination should begin 900 ± 100 milliseconds
after the peak of the first tone.
3.4.4 Sequence Control
Five tone sequence control lines should be provided to actuate
individual or two tone sequences as follows:
a. Passenger Call (High Tone)
b. Attendant Call (High/Low Tone)
c. Attendant Emergency Call (High/Low Tone Repeated Three Times)
d. Seat Belt Sign (Low Tone)
e. Smoking Sign (Low Tone)

That's a pretty exacting standard! It certainly explains why they all sound the same regardless of the aircraft and avionics manufacturers.

Love how an otherwise quite technical specification requires the tones to be "of a pleasant sounding musical nature".


text:
Which specific version of English are international pilots and ATC required/recommended to learn?
Are international ATC and pilots technically required to learn British English, American English, or something else? I've heard it said that they are "supposed to speak ICAO standard phraseology, which just happens to be made up of English words," and that many ATC and pilots speak precisely as many English words as they need to scrape by. Even if they aren't explicitly required to speak AmE or BrE, they are still indirectly required to speak whichever version ICAO standard phraseology is based on, so if that is the case, which version would this be?
Some other things that I'm not asking about directly but might be helpful in providing a complete answer: a bit more about ICAO standard phraseology - is it considered a separate "controlled language" like Simplified Technical English, which was incidentally (or maybe not) developed for use in aviation maintenance manuals? Is it a subset of STE?

It isn't conversational English, so it really doesn't matter if you call it American or British. I would say it is a technical English or subset of English. Either way one who understands American English should be able to understand British English and vice-versa, since idioms and "turns of phrases" are not used. I don't need to know what a bonnet is (in reference to a car) or a Lorry, but I do know what queue means even though Americans don't typically say "queue" in reference to waiting in a line...

"Neither" is an answer, too, I guess. I'm really fishing for historical trivia rather than practical information, though.

The FAA bases English proficiency on the ICAO Level 4 English Language Proficiency Criteria, which don't mention any particular dialect or variant of English. Instead, they focus on the speaker's ability to communicate and they explicitly accept that the speaker may make mistakes (emphasis mine):

Pronunciation, stress, rhythm, and intonation are influenced by the
  applicant’s first language, but only sometimes interfere with ease
  of understanding.
  [...]
  Basic grammatical structures and sentence patterns are used creatively
  and are usually well controlled by the applicant. Errors may
  occur, particularly in unusual or unexpected circumstances, but
  rarely interfere with meaning.
  [...]
  There may be occasional loss of fluency [...] but this does not
  prevent effective communication

It's clear that ICAO doesn't expect non-native speakers to be fully fluent, and once you accept that then there's no benefit at all in trying to enforce a particular dialect. Using standard vocabulary and phrases is the real key to effective technical communication, and you can see that in many other professional contexts too.
I've met plenty of non-English speakers who can speak effectively but not fluently about a specific technical domain, but they still don't have the vocabulary to talk about their holiday plans or other 'trivial' topics. Asking what dialect of English those people speak is fairly meaningless, but Globish might be the best answer :-)

Preamble
Declaring an emergency would be one of the most critical conversations, however it would be limited to something like this:

 Pilot: MAYDAY, MAYDAY, MAYDAY, Metro Control, Big Jet 345, main electric failure, request immediate landing at Metro, position 35 miles north
  west of Metro, heading 120 flight level 80 descending, 150 persons on board, endurance three  hours. ATC: Big Jet 345, Roger the MAYDAY, turn left heading 090, radar vectors ILS  runway 27. Pilot: Big Jet 345 request runway 09. ATC: Big Jet 345, roger, turn  right heading 140 for radar vectoring runway 09, descend to 3000 feet, QNH 995, report established. Pilot: Big Jet 345, heading 140, descend to 3000 feet QNH 995, report established localiser runway 09.

The vocabulary and the grammar used are very simple and the exchange takes advantage of the prescribed phraseology.
ICAO Chicago Convention, Annex 10. recommends using English and the local language. For both languages, local dialects are accepted as the norm. So for English there is indeed no reference to British or American, or any other variation.
Since 2003, ICAO recommends to member States to check for languages proficiency, setting the minimum acceptable level to 4. Actual and detailed requirements are found in Appendix 1 of Annex 1.
Annex 1, Appendix 1
Describes two types of criteria used to evaluate proficiency: An overall understanding, and explicit details.

To meet the language proficiency requirements contained in Chapter 1, Section 1.2.9, an applicant for a licence or a licence holder shall
  demonstrate, in a manner acceptable to the Licensing Authority,
  compliance with the holistic descriptors at Section 2 and with the
  ICAO Operational Level (Level 4) of the ICAO Language Proficiency
  Rating Scale in Attachment A.

Overall criteria allows for different dialects and accents:

2. Holistic descriptors. Proficient speakers shall:  [...] e) use a dialect or accent which is intelligible to the aeronautical
  community.

Detailed scale is found in Attachment A, ICAO language proficiency rating scale. I show here only levels 4 to 6, as 4 is the minimum expected for operational personnel.

1.1 Expert, extended and operational levels
ICAO member States have agreed on a set of standard phrases that must be used instead of plain language, plain language is used only when this phraseology is not effective. There is no requirement, for crew and controllers, to study the language like an interpreter would do, they just need to be understandable.
To understand the type of conversation used in regular communications:

SKYbrary Phraseology summary with examples,
ICAO Manual of radiotelephony (doc 9432).

Chicago Convention is used at national level by member States. When recommendations are not exactly followed, this is mentioned in the local AIP, section GEN 1.7 Differences from ICAO Standards, Recommended Practices and Procedures. AIPs links can be found on this Wikipedia page.
The next paragraphs just provide the references in ICAO documentation. You may skip them if not interested.

ICAO documents can be downloaded from the the Switzerland Federal Office of Civil Aviation, on this page (in French).
Annex 10
Standardized phraseology must be used before plain language.

5.1.1.1 ICAO standardized phraseology shall be used in all situations
  for which it has been specified. Only when standardized
  phraseology cannot serve an intended transmission, plain language
  shall be used. [...] Detailed language proficiency requirements appear
  in the Appendix to Annex 1.

Samples of ICAO standard phraseology found in Annex 10 (standard phrases are uppercase):

5.2.1.5.8 The following words and phrases shall be used in radiotelephony communications as appropriate and shall have the
  meaning ascribed hereunder: [...]

CONFIRM • “I request verification
  of: (clearance, instruction, action, information).”
CONTACT • “Establish communications with...”
CORRECT • “True” or “Accurate”.
CORRECTION • “An error has been made in this transmission (or
  message indicated). The correct version is...”
DISREGARD • “Ignore.”
HOW DO YOU READ • “What is the readability of my
  transmission?”
I SAY AGAIN • “I repeat for clarity or emphasis.”
MAINTAIN • “Continue in accordance with the condition(s) specified”
  or in its literal sense, e.g. “Maintain VFR”.
NEGATIVE • “No” or
  “Permission not granted” or “That is not correct” or “Not capable”.

For the crews, two languages are available.

5.2.1.2.1 The air-ground radiotelephony communications shall be conducted in the language normally used by the station on the ground
  or in the English language.
5.2.1.2.2 The English language shall be available, on request from any
  aircraft station, at all stations on the ground serving designated
  airports and routes used by international air services.

Pronunciation differences are taken into account, and there is a standardized pronunciation to be used for critical elements, like when spelling words and numbers, including when using English.

5.2.1.3 Word spelling in radiotelephony. [...] The pronunciation of the words in the alphabet as well as numbers may vary according to the
  language habits of the speakers. In order to eliminate wide variations
  in pronunciation, posters illustrating the desired pronunciation are
  available from ICAO.
5.2.1.4.3.1 When the language used for communication is English, numbers shall be transmitted using the following pronunciation [...]

Annex 1
In 2003 ICAO adjusted its Annex 1 to the Chicago Convention to add language proficiency requirements:

Amendment of definitions; new provisions requiring language
  proficiency for aeroplane and helicopter pilots, navigators using
  radiotelephony, air traffic controllers and aeronautical station
  operators; introduction of a Note on qualification and training for
  aeronautical  meteorology personnel; amendment to the Human Factors
  knowledge requirements  for Aircraft Maintenance Engineer.

This includes a requirement to demonstrate language proficiency, both for crews...

1.2.9.1 Aeroplane, airship, helicopter and powered-lift pilots and those flight navigators who are required to use the radio telephone
  aboard an aircraft shall demonstrate the ability to speak and
  understand the language used for radiotelephony communications.

and for ATCO.

1.2.9.2 Air traffic controllers and aeronautical station operators shall demonstrate the ability to speak and understand the language
  used for radiotelephony communications.

This proficiency has to be evaluated against a common scale.

1.2.9.4 As of 5 March 2008, aeroplane, airship, helicopter and powered-lift pilots, air traffic controllers and aeronautical station
  operators shall demonstrate the ability to speak and understand the
  language used for radiotelephony communications to the level specified
  in the language proficiency requirements in Appendix 1.

Those that don't match the highest level will be checked again and again...

1.2.9.7 Recommendation.— The language proficiency of aeroplane, airship, helicopter and powered-lift pilots, flight navigators
  required to use the radiotelephone aboard an aircraft, air traffic
  controllers and aeronautical  station operators who demonstrate
  proficiency below the Expert Level (Level 6) should be formally
  evaluated at intervals.

But the natives and assimilated won't be bothered. They just need to show they are understandable by the international aeronautical community.

Formal evaluation is not required for applicants who demonstrate expert language proficiency, e.g. native and  very proficient
  non-native speakers with a dialect or accent intelligible to the
  international aeronautical community.

※

There is actually a name for the subset of English that is used in aviation: Aviation English. However, it is not an official standard, but a name applied to the subset of English that is derived from the widely accepted ICAO recommendation to use English.
Note that Aviation English does not specify an accent (American or British or any other). The ICAO standard phraseology words have been specifically chosen to minimise confusion that might be caused by different accents.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
How do ATC radars know where to position a primary target?
Primary target: An aircraft not reporting mode-C, the only thing the controller has is the return on the radar.
When a controller reports a primary target as traffic to other aircraft, the controller does not have the altitude of the target. Given this, I conclude that ATC radar does not have the altitude (angle-up) to the target, and only provides azimuth.
So then without the altitude, how does the radar-system know where to put the target laterally on the screen?
Example, a radar picks up a target that is 10 miles from the station. If the target is 0 AGL, the proper position would be 10 miles out. However, if the target is at 15,000ft, the proper position would be 9.5 miles out.
Since the difference is so small, does the radar just put the target at 10 miles, and the FAA separation guidelines factor in the discrepancy?

If the target is at 15000 and the station is at 0, then the slant range will be LONGER.

Primary radar, even modern digital systems, do not give any possibility to the controller to determine altitude.  The digital system has that capability, but civil ATC does not.
In primary radar displays usually just the azimuth and range are plotted. So an aircraft at 15.000 ft 9.5 NM away will be plotted on 10 NM distance, just like an aircraft at 0 ft 10NM away. Usually the secondary radar is collocated with the primary so secondary targets can be displayed using the same projection (disregarding the altitude).
If you now apply horizontal separation based on this projection, you will never bust the separation minima. It is a conservative way of providing separation, but when there is no altitude information it is the best possible way.

Note that this does not only apply to primary targets, but also to Mode-A only targets

Do you have a primary source/reference for this? I do know that some radar systems are capable of determining altitude (e.g., military). I'm wondering if ATC systems can to some extent, and could use it to adjust slant range, even if it's not accurate enough to display or use for separation purposes. I'd like to read more from an authoritative source. I don't doubt your answer though; reading your bio it sounds as if you likely know what you're talking about in this area :)

@dvnrrs I am not sure where to find an official reference quickly, but this might help. Modern primary radar systems determine elevation angle as well, wich combined with a meteo model and corrections for the curvature of earth's surface can help to determine the altitude of an aircraft. This helps especially if you are fusing radar data from multiple radars and other surveillance systems (multisensor tracking). In such cases simple projections don't work.

Good enough... thanks for the link and good answer!

@dvnrrs another way to determine altitude is with another radar pass doing RHI scans (constant azimuth, varying elevation).  ATC radar doesn't have the motors to do this though (and no electronic beam steering either).

Primary radar returns, in complete absence of secondary radar data (transponder A, C, S, etc. and ADS-B type data), will display slant range.  Some military radar can provide elevation data, for example PAR radar, and using range and elevation, the height of a return can be inferred.
Secondary systems, such as Mode-C and Mode-S transponders, and ADS-B report pressure altitude of the transponder's altimeter, and are used to determine altitude. These schemes do not really rely on radar, but rather on barometric data, GPS data or both, to provide an altitude.  In civilian ATC it is generally considered that pressure altitude is adequate.
So the answer is: 1. Using only primary radar, the range on the radar screen is based upon slant range to the target.  2. There may be range errors relative to a planar datum due to the fact that slant range of a target at the datum may be accurate, but the slant range of a target at altitude will be greater. [Simple trig may be employed to calculate that error. Eg 10nm ~= 60000 feet, and would be the slant range at the same elevation as the radar station.  A plane at 60,000 feet, directly above a point 10 nm from the station, will show a slant range of 1.414 * 60,000 feet or about 14 nm.]

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
If propeller-driven planes with electric engine became the norm, would descent for landing with the engines turned off become a routine procedure?
To elaborate on the question: I know that in modern fossil fuel-driven aircraft turning the engines off during descent and/or landing approach isn't feasible for safety reasons (which makes total sense to me) - but, given that electric engines are quite easy/quick to turn on & off  compared to toboprops and turbofans, is it  likely that lowering altitude with the engines turned off for a big portion of the descent (let's say, untill an arbitrary altitude would be reached, e.g. 500m or something along those lines) would become a norm in the airline industry?

The props would need to be fully featherable - otherwise the non-spinning prop blades would create a lot of drag; or the wind blowing would force the props to spin and reverse drive the electric motor, which would also create drag if that was used to create electricity to recharge the batteries, similar to regenerative braking in electric cars.

@CrossRoads during decent that could be desirable, use the potential and kinetic energy to recoup some electrical energy like hybrid cars do.

Could be - very situation dependent tho.

It's unlikely the pilot would be switching the "propulsion master" off, but it's very probable that "idle power" on the throttle or thrust lever would in fact be a stopped or stopped/feathered motor.  It's likely that regen braking would be electrically available, but it's probably something you wouldn't want to use in flight, for the same reasons you don't engage reverse thrust on jet engines before touchdown (in fact, there are some aircraft where you do, for a subset of the engines, in part because of the time needed to engage reversers).
Having instant throttle response available is very important, so "off" shouldn't be the same "off" you'd use when parking and tying down -- but having genuinely zero thrust could be useful for certain kinds of approaches (others, you want/need to carry some power to ensure you stay enough above stall to maneuver without steepening the glide slope).

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is that protruding fuselage part?

Circled in red above, I suspect that's a high-lift device meant to improve handling at takeoffs and landings, but I don't know for sure really. What is its name and uses?

I think that's a sort of running-board for Tom Cruise to stand on.

+1 hand-drawn red circle!

The strakes function as giant vortex generators.  They generate vortices at high AOAs to improve airflow over the rudder at low speeds.  During the Q400 test program it was found that there was some local flow separation at the lower area of the rudder (reducing rudder power and possibly creating unpleasant vibration) and this is a classic, relatively hassle-free, aerodynamic band-aid kind of add-on to address the problem without major redesign.  You don't see them on the shorter -8s.
Strakes and Vortex Generators work by creating a horizontal tornado so to speak, with the outer half of the tornado in the free stream.  This has the effect of pulling smooth free stream air into the turbulent air close to the surface, which, even though it's spiraling, is better than the random turbulent flow that is there otherwise.
You sometimes see similar strakes on the upper aft fuselage on light aircraft just ahead of the fin, like on a Chipmunk.  These are to improve spin characteristics by generating a vortice over the rudder when AOA is high as in a stall/spin.  They call them "spin strakes" in that case.

They are typically called "strakes" are there to improve handling by minimizing unwanted rolling tendencies. I think the plane is an Bombadier Dash-8
Wikipedia article with more pictures: https://en.wikipedia.org/wiki/Bombardier_Dash_8
You can see them on this Q400 planform

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the effect of wing flex on wing's airfoil shape and its performance effect on wing?
There are good amount of discussion on wing flex in this forum.
I am more interested in understanding the effect of flex on aerofoil shape of the wing and its impact on flight performance.
Do designers take into account the cross sectional shape change induced by wing flex while designing the aircraft? If not, is it because the effects are negligible or simply too complicated to simulate?
Also, does the shape change induced by wing flex help in improving the performance?


text:
Is this Class G Airspace?
So it's been about a decade since I got my private pilot cert and almost as long since I got to fly. My map reading is a little rusty.
I'm trying to fly my drone at a local park and it's warning me that I'm in Class D airspace. I've marked on the map where the park is.

If I'm reading this correctly, then I should be in Class G airspace up to 700ft AGL
Am I missing something or is this probably just a bad GPS signal on start?
I'm not getting repeated warnings so I think it's a bad signal but I figured a prudent pilot would check.

As the answers have correctly noted, that location on the chart is Class G at the surface. However, do note that if you are flying your drone under 14 CFR 101, the recreational model aircraft rule, you will need to contact the tower: "(e) When flown within 5 miles of an airport, the operator of the aircraft provides the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport) with prior notice of the operation." Lakewood park is 4.8 NM from the runway at KBKL.

@JWalters I think you're mistaken KBKL to 413004N0814728W = 5nm  https://www.google.com/maps/place/41%C2%B030'04.2%22N+81%C2%B047'28.2%22W/@41.4980851,-81.7956728,16z/data=!4m5!3m4!1s0x0:0x0!8m2!3d41.5011667!4d-81.7911667

I'm not sure what point you are referring to; the link takes me to a point in lake Erie north of Lakewood park. From that point to the runway at KBKL is a distance of 4.49 NM (5.167 SM).

@jwalters the point that I marked on the map is north east of Lakewood park just slightly and it's 5 nm from KBKL. You can put the coords I pasted into sky vector and see. Also I called the KBKL Tower and not only do they have no clue where Lakewood park is, they made it clear they didn't care.

Ah, I see what you did. You are referencing the distance from the ARP (Airport Reference Point) which is generally the average center of all runways. In this case BKL's ARP is just east of twy D, roughly 3100 ft from the western end of the long runway, and 4.97 NM from the point you designated. The reg requires you to contact ATC and the airport operator if within 5 miles of the "airport", not the center of the airport or the ARP. Try that kind of measurement form KDEN to see why the difference is significant.

Provided the drone is flying where the red dot is, you are correct and Class G extends from the surface to 700 ft AGL.  If you really wanted to play it safe, call the tower at KBKL to establish two way radio comms before flying there.

Note that under FCC regulations, calling the tower using airband radio requires you to have a radio license, unless you're aboard an aircraft.

You don't even have to use a radio.  They usually publish telephone numbers for control towers in the Chart Supplements.

I don't know drone laws, but are you allowed to fly within the transponder ring of a class B without one?

@TannerSwett OP says they have a "private pilot cert", so presumably they have a radio license.

@aCVn As far as I know, most private pilots in the US don't have radio licenses. US pilots don't need a radio license unless they're flying internationally, or transmitting while not aboard an aircraft (47 CFR 87.18(b)).

@TannerSwett Interesting. That'd definitely be a big difference from how it is in EASA-land, then (where, IIRC, one needs a radiotelephony certificate no later than by the time one flies solo, to be allowed to use the radio aboard the aircraft; certainly by the time one is no longer a student pilot in training).

Yes you are in Class G at that location.  The shaded red band indicates the floor of Class E airspace  extends down to 700 AGL at that location, and the floor of theshelf of Class B airspace is 1900 MSL above you.  The ground elevation is roughly 640 MSL according to the tower data nearby.  I agree that a call to the tower to verify would be prudent.

Yes, you're reading the chart correctly.  Either your drone's GPS is off by quite a bit, or it was deliberately designed to be overly sensitive so that you couldn't accidentally fly into nearby controlled airspace.


text:
How do VTOL aircraft like the V-22 Osprey not tilt?
How do aircraft like the V-22 not tilt under an unbalanced load? if they are only supported by 2 forces on either side a large weight in the back should cause it to lean backward when stationary, should it not? its hard to put this into an image but here goes nothing:

A large weight in the back would surely cause it to lean; original image source

Weight and Balance is a consideration for all aircraft, not just the Osprey.
If the weight is distributed out-of-bounds, this would be a problem.   So, they distribute the load appropriately.

Why do you think your question is specific to the Osprey? Any aircraft would behave in the same way.

Most airplanes use the (inverse) lift generated by the tailplane to balance, but this isn't applicable during VTOL.

It happens that there is something known as a Centre of Gravity which also serves as the centre of rotation and that is located in line with the wings.

Is it possible the question that was meant to be asked is "how is pitch controlled for a tilt rotor aircraft in hovering and slow flight"?

I think the poster is wondering how the Osprey maintains this balance while changing the pitch of the rotors.

If you think about it, your question applies in exactly the same way to a conventional helicopter. You might expect that it would pitch nose-down if the weight is forward, and nose-up if the weight is aft. In fact, it's even worse for a conventional helicopter, because with only one rotor it would roll (tilt left-right) as well as pitch.
The answer is the same for the Osprey as for a conventional helicopter: the pitch is controlled by cyclic control of the rotor. As the rotor spins, a mechanism inside it changes the angle of attack of the blade (the pitch of the blade) as it rotates. This change can cause it to generate more lift when it's at the rear than at the front (or vice-versa, or left-to-right). This creates a turning moment about the centre of the rotor disk, which counteracts the moment of the unbalanced weight.
You only get so much of a moment with it, though. The aircraft needs that moment in order to change its pitch to manoeuvre. If you had to use the full range of blade pitch (the maximum cyclic control) just to counteract the unbalanced weight, you wouldn't be able to pitch the aircraft any further in that direction. For this reason, the maximum moment of rotorcraft (how far the centre of mass can be away from the centre of lift) is typically smaller than for airplanes.

Elevator on aircraft has same issue when aircraft slows down!  The olde Chinook twin rotor (front and back) helicopter can add or subtract power to compensate for a wide range of cargo CG points, but the V-22 Osprey is much faster.

According to various bits of online documentation, the rotors have cyclic pitch control like a helicopter as well as collective pitch control like a helicopter and most high-performance propeller airplanes (often referred to as having a "variable pitch" propeller). The cyclic on the Osprey is controlled with a swashplate that apparently has only front-to-back cyclic control since side-to-side is not needed. To move sideways, the Osprey would simply increase the collective pitch of one rotor while reducing the collective of the other. Here's a passage from one document I found:

Specifically by axis, pitch is controlled through longitudinal cyclic,
lateral control is obtained through differential collective combined
with lateral cyclic, and height control is via symmetric collective
commands.

So it works like a typical helicopter and the lift can be adjusted as needed to deal with a variable center of gravity.

I suppose it could, if improperly loaded.  But V-22s, like any other aircraft, have weight and balance envelopes to prevent this from happening.  And any competent loadmaster and flight crew would load the aircraft accordingly and double check it prior to flight.

The weight and balance envelope is a specification and prevents nothing. It is simply a chart on a piece of paper that tells the pilot the acceptable range of center of gravity such that the actual controls of the airplane can keep it flying. The question was about how the actual flight controls work so that there is an envelope and not just a single point for the center of gravity. For instance, the elevators on a conventional airplane control the center of lift to account for a variable center of gravity. What does the V-22 have to accomplish that when it is hovering? That was the question.

No, the weight and balance envelope is a design criteria for range in which the aircraft center of mass must lie within to ensure controllability and stability as designed.

And still, the question was about how the pilot controls the aircraft, and the weight and balance specification, design criteria, or whatever you want to call it, is not something that controls the aircraft in flight. The cyclic pitch control on the prop-rotors controls the lift such that the center of lift is made to align with the center of gravity to keep the aircraft from tipping. I'm sure that we can both present our pilot's licenses as a statement of authority but I'd rather just try to understand the original question which was about how the pilot can control the aircraft in flight.


text:
Does the minimum power required for level flight depend on CD0?
I came across this video few days back on Edx 16.101 youtube channel.

At 7.00 min of the video, the presenter derived an equation for minimum flight power which does not depend on Cd0.
$$P_\min = \frac{4}{3\pi e AR}  \sqrt{\frac{2W^3CL}{\rho S}}$$
I don't have a doubt on the derivation, but this result seems to be very contradictory for me.
For example, let's take 2 identical aircrafts, one with fuselage airbrakes deployed and one without. (Identical CL, AR, $\rho$, S, CL and e but different Cd0)
According to this expression the power requered cannot change. But,

For same CL, V is going to be the same
With airbrakes deployed, aircraft 1 drag is much higher than the aircraft 2
Power required (D*V) should be higher for aircraft 1.

May be I am missing something simple. Why is this apparent contradiction?

I think what you're missing is that the CL will not remain the same between the two aircraft.

To expand on what @Porcupine911 said, two identical aircraft, one with flaps up, one with flaps down, have different CL.

Hi Porcupine, It cannot be the case, as clearly the Pmin is a function of CL. CL is given to evaluate the Pmin. one possible answer is that for different Cd0, 2 aircrafts has 2 speeds. but for same CL even that cannot be the case. Anyway thanks for the input. appreciate it ..

Thank you for the excellent question!
The whole expression is only valid for the optimum polar point where the ratio $\frac{c^2_D}{c^3_L}$ reaches its maximum. If you deflect spoilers, this optimum will shift to a higher lift coefficient, so both aircraft will not fly at the same lift coefficient or the same speed any more! Always keep in mind that in this special condition the lift coefficient can also be expressed as
$$c_L=\sqrt{3\cdot\pi\cdot AR\cdot e\cdot c_{D0}}$$
Just plug that back into the equation and the minimum power expression will make a whole lot more sense:
$$P_{min}=\frac{4}{3\cdot\pi\cdot AR\cdot e}\cdot\sqrt{\frac{2\cdot W^3\cdot\sqrt{3\cdot\pi\cdot AR\cdot e\cdot c_{D0}}}{\rho\cdot S}}$$
This is still the same equation, but now it should be obvious that opening the spoilers will require more power.

Also, presumably, this ignores all other extra drag by the fuselage, vertical stabilisers, engine pylons etc. As the edited question asks why two planes with identical wings but different fuselage (one with airbrakes deployed, like SU-27, one without) require the same amount of power to stay level. The question could perhaps be simplified to: if we have two identical airplanes but one drags along a large parachute why wouldn't the plane dragging the parachute require more power to fly?

@slebetman: It will require more power to fly, only the equation does not make this obvious. When expressing the same formula differently, the added drag shows up. Regarding fuselage, stabilizers etc: This is all included in the zero-lift drag. The equations are valid for the full airplane, not just the wing.

@slebetman, no, it does not ignore anything. If I understand correctly, the logic is that minimum drag at the point where induced drag equals form drag, so they replace the total drag with twice the induced drag and express that in terms of lift coefficient. And what Peter does in the second equation is replacing the total drag with twice the form drag and express that in terms of drag coefficient.


text:
In 1982 Admiral Grace Hopper said "I still haven't found out why helicopter rotors go the way they do". If she were here today, how might one answer?
After about 24:50 in the video NSA Releases Internal 1982 Lecture by Computing Pioneer Rear Admiral Grace Hopper Admiral Hopper says:

...Now when it comes to carousels at airports I can see a good reason why they run this way that's because most people are right-handed - that's the way you grab your bag. I still haven't found out why helicopter rotors go the way they do, but um... I find it rather
interesting that that we've always done it this way seems to be so much embedded in things. And it's the most dangerous phrase you can use in a computer installation.

Question: In 1982 Admiral Grace Hopper said "I still haven't found out why helicopter rotors go the way they do". If she were here today, how might one answer?
Is it like her example of clocks, in that they could go in either direction and it's just a convention, or based on history, or is the direction of rotation chosen for some specific reason(s)?
"Bonus points" to address if there'd be any problems with building and selling helicopters today that spun the opposite direction (other than marketing).

Her point is that in computer installation you should think about every decision and not just do things as they have "always" been done.

@PeterKämpf Indeed, I watched the video with rapt attention, and applied her message (one of many in the video) to helicopter helicity. "Is it like her example of clocks, in that they could go in either direction and it's just a convention, or based on history, or is the direction of rotation chosen for some specific reason(s)?" I would guess that each time Bell introduced a new model, they didn't choose the same helicity just because they've always done it that way, but indeed for "marketing" reasons; the training overhead and general confusion would be a barrier to entry.

@PeterKämpf while it is "the way we've always done it", there are good reasons to opt for the same helicity as previous models. I wanted to see if they went beyond backwards compatibility or not. It seems they don't.

For clocks in particular - in the northern hemisphere, if you put a pole in the ground its shadow will rotate clockwise through the day, as does the sun itself in the sky.

Interestingly today we still have no good reason for doing it one way or another. It's just mostly how it's always been done at a particular company. The problem is once you start doing things one way a lot of your parts and tooling are designed for the way you normally do things so it's hard for a company to do both. Their competitors though are free to do it the other way.

@PartyArk now how the heck does the Sun know to go clockwise?

@uhoh I think it's much easier to explain why the sun knows to go clockwise than to explain why most humans know to be born right-handed. So if "most humans are right-handed" is an example of a good reason of suitcase carousels, "sun goes clockwise where most land is" seems to be even a better reason for clocks. So its a bit weird to use clocks as an example of arbitrary convention while using carousels as an example of a convention with a reason.

@JiK I was being humorous/ironic, but I do see what you mean, if one sees sundials and mechanical clocks as both kinds of clocks. To me they are apples and oranges. There's no connection. One's mechanical, indoors, vertical, and has moving needles, the other is sculptural, outdoors, horizontal, and has no moving parts whatsoever. Since mathematical convention for rotation is counterclockwise (right hand rule, the slope of the line is measured from the x axis ccw to the y axis) I think clocks all turn the wrong way.

@uhoh, please accept my answer if it helped to find your answer ^_^

@AadirajAnil thanks for the reminder. I usually wait several weeks before accepting so as not to discourage additional answers, and the bump to the active queue that happens on accept is more effective at bringing the answer to additional readers' attention is more effective if some time has gone by. Since several weeks have indeed gone by and no additional answers have been posted, then your answer is "ripe" for accepting :-)

It's a convention and both clockwise and counterclockwise work fine because the blade can be designed for either.
The direction of rotation of helicopter rotors is somewhat standardized but varies between manufacturers. American helicopters like those made by Bell and Sikorsky have counterclockwise-rotating main rotors (from above), while a few European helicopters, like some French (Eurocopter Tiger) and Russian models (Mil Mi-8), rotate clockwise.
It's not entirely a Europe vs North America thing because some European manufacturers such as AgustaWestland AW101 and AgustaWestland A109 have counterclockwise-rotating rotors. German and Japanese manufacturers such as MBB (Germany) and Kawasaki (Japan) also have counterclockwise rotating rotors.
Historically speaking it is often attributed to the Sikorsky R4 which began this counterclockwise rotor convention. Westland in the UK and Agusta in Italy as well as the Japanese manufacturers Mitsubishi, and Kawasaki all entered the helicopter market by making licensing agreements to build American designs so this design language was carried across and is the norm now.
One more reason countries have localized standards is because the pilots would need to be retrained and use a different muscle memory for rotors spinning in different directions. I'd think this would be quite difficult.
Here's a diagram on this (LE marks leading edge) -

(Source)
So basically there's helicopters that spin the rotor in both directions, but in one place, it is more likely you'll only see one or the other.

Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed.

One or the other, or both directions on the same helicopter: see Chinooks, Kaman K-Max, etc


text:
Was ASRS report volume ~constant 1990 - 2005, nearly triple by 2015 then remain ~constant until 2023? If so, why is that thought to be so?

above: Screenshot from "Voluntary Data Contributions to Information Sharing August 9-10, 2016 Aviation Safety Reporting System (ASRS),  Linda Connell" annotated to guide the eye and include data point from a different source in 2023.

Sept. 14 2023 NASA Press Release (23-106) UPDATE: NASA Shares UAP Independent Study Report; Names Director includes

https://go.nasa.gov/3PED0qv

which then sends readers to the 2023 NASA Unidentified Anomalous Phenomena Independent Study Team Report which says:

Finally, the threat to U.S. airspace safety posed by UAP is self-evident. The
panel finds that a particularly promising avenue for deeper integration within
a systematic, evidenced-based framework for UAP is the Aviation Safety
Reporting System (ASRS), which NASA administers for the FAA. This confidential and voluntary reporting system for pilots, air traffic controllers, and
other professional aviation staff, receives approximately 100,000 reports per
year.

Reading further I found this 2016 NASA ASRS Program Overview at (surprisingly) ttsb.gov.tw I assume there are copies of the presentation elsewhere but I couldn't find them.
Below are screenshots from slides 1 (for identification) and slide 22 "ASRS Report Volume Profile". It depicts rates of reports ramp from a few hundred to roughly 3,000 per month by 1990, stay roughly constant until about 2005, then begin what looks to me to be an at least quadratic if not exponential increase, almost trippling to 8,000 per month in 2015.
If the 2023 NASA report block quote is accurate and I'm interpreting it correctly, the rate is currently about 8,000 per month - about the same as it was in 2015.
Question: Was ASRS monthly report volume roughly constant between 1990 and 2005 almost triple between 2005 and 2015 and then again remain about constant until 2023? If so, why is that thought to be so?
Potentially helpful:

https://en.wikipedia.org/wiki/Aviation_Safety_Reporting_System
https://asrs.arc.nasa.gov/

Screenshots of slides 1 and 22 (click for full size):

slightly related Is there a website with a list of all commercial airline incidents? and in meta Which website should we prefer to reference to aviation accident/incidents summaries?

I didn't find a tag for "reporting" but welcome help with tagging

anecdotally, I remember some kind of grassroots marketing push for "NASA reporting" when I was in flight school, which would roughly coincide with the second surge.  I recall a lot of emphasis on it not being a mechanism for laying blame and instead being for improving safety

Since when can these reports be made online? Since when do mobile phones have good access to internet, so quick reporting was even easier? I wouldn't be surprised if there is a connection between these.

@DeltaLima Thanks for expanding your comment into a (quite thorough) answer.

According to NASA's website in 2016 on the 40th aniversary of the ASRS reporting:

Since 2006, all reports are logged and processed with full anonymity
and that de-identified data has been accessible to the public. In the
last 10 years, the ASRS Database has had more than 189,000 queries.

Furthermore, I found the September/October 2005 edition of CALLBACK (ASRS Reporting Bulletin),  which announces the introduction of email supscription to the reporting, furthermore increasing accessibility to the data.

We will be encouraging readers to sign up for the e-mail service
(still FREE) in lieu of the printed copy. We will continue to offer a
print version for those who want to continue receiving paper copies.

It also announces the start of the Electronic Report Submission :

Electronic Report Submission (ERS) is close to roll out. In addition
to the obvious benefits for reporters, ERS will  streamline report
handling for greater efficiency and reduce ASRS processing costs.

The January 2007 edition of CALLBACK anounces ERS is now accessible online:

You’ve had a brief introduction to two new ASRS  services in recent
issues of CALLBACK – Electronic  Report Submission (ERS) and the ASRS
Database  Online. Now we’d like to give you more information  about
both, and explain how you can begin  accessing these new services
through the ASRS web  site at: http://asrs.arc.nasa.gov

So between the end of 2005 and beginning of 2007 the following changed:

reports were now logged and processed with full anonymity
reports could be submitted electronically
de-identified data has been accessible to the public
subscription to the ASRS bulletin could be done via email

Full anonymity would lower the barrier that people feel to make the report, electronic submission would make it even easier, whilst making de-identified data accessible to the public and email subscription to the ASRS bulletin would increase the general awareness of ASRS existence.
This started to drive the growth of the ASRS reporting rate, further accelerated by the improvement in mobile internet accessibility lowering the reporting barrier even more.

I found a presentation from July 2023, showing the full graph of report intake from January 1981 until December 2022 on page 13.

This shows that after 2015, the growth of reporting rate reduced, with the peak of reporting rate in 2019 at about 9000 reports per month.
It seems that by 2015, ASRS was so widely known that the awareness is saturating and the growth stagnates.
During COVID the rate fell by about 35%, and came back to 2015 levels of approximately 8000 reports per month in December 2022. Since air traffic levels were still below the 2019 level, this is not unexpected.


text:
What happens procedurally when a country's airlines are now allowed to fly through another country's airspace for the first time? (new flight routes?)
CNN's July 15, 2022 Saudi Arabia opens airspace to Israeli flights begins

Saudi Arabia on Friday opened its airspace to all civilian carriers, including all flights to and from Israel, in a step toward normalizing relations between the two nations as US President Joe Biden tours the Middle East.
In a statement shared hours before he was due to fly directly from Israel to Saudi Arabia, Biden hailed the kingdom's decision, saying that it could "help build momentum toward Israel's further integration into the region."

and later

The move fully overturns the decades-long ban on Israeli overflights in Saudi airspace. Israeli airlines flying to Asian routes like India and China previously had to take a detour around Saudi Arabia that added hours to the journey.
Saudi's General Authority of Civil Aviation (GACA) on Thursday said in a statement that it had decided to open its airspace for all air carriers "that meet the requirements of the Authority for overflying." It added that the country is keen "to fulfill its obligations under the Chicago Convention of 1944, which stipulates non-discrimination between civil aircrafts used in international air navigation."

Presumably not much will happen in the air immediately, but economic pressure on "Israeli airlines flying to Asian routes like India and China" makes recovering those added "hours to the journey" attractive.
From a practical standpoint what happens when an airline considers making significant changes to the routes of some of their flights that include overflights they were previously not allowed? Do they calculate and evaluate some alternatives, choose two or three they like then propose them to some regulatory body and to the new country they will overfly and try to get a consensus? Are there historical models of this sort of thing that serve as instructive examples?
Question: What happens procedurally when a country's airlines are now allowed to fly through another country's airspace for the first time? How are the new flight routes selected and agreed upon?

I don't know if there is a tag specific for one country's denial of airspace towards another country's airlines, help with tagging welcomed.

I doubt it's half as complicated as you think.  From a pilot's perspective, just file direct and go.  There may be some high altitude jet route intersections and preferred routing to satisfy ATC, but dispatchers will factor that into any preloaded flight plans for regularly serviced routes.  Although I can't predict how the Saudis might manage the transition...

Saudi Arabia already grants overflight permission for aircraft from many countries, so all Israeli aircraft will have to do is follow the documented rules and avoid any prohibited areas like Mecca, for example. It's not going to be much different than what they do now.


text:
What is Flexible Gunnery in the US Air Force?
I read many times in English Wikipedia that some servicemen were trained in Flexible Gunnery schools, but I don't get what that exactly means.
Example:

In January 1942, the 2d Air Force was withdrawn from the Western Defense Command and assigned the operational training of units, crews, and replacements for bombardment, fighter, and reconnaissance operations. It received graduates from Army Air Forces Training Command flight schools; navigator training; flexible gunnery schools and various technical schools, organized them into newly activated combat groups and squadrons, and conducted operational unit training (OTU) and replacement training (RTU) to prepare groups and replacements for deployment overseas to combat theaters.

Could you add a link to an example article where the term showed up? Thanks, and welcome to Aviation.se.

Of course I will: https://it.m.wikipedia.org/wiki/Second_Air_Force. That's it, look up in the "Storia" section, you'll find che "armi brandeggiabili" )that's plural form) mentioned. Very obliged for your helping, thanks a lot.

(And, of course, I found the "flexible gunnery" in the corresponding en.wiki article, which I happen to be translating.)


text:
What is this NASA UAV, and what is its function?
For the question What's up with the “What's Up at Wallops” app? I was reviewing the What's up at Wallops website and drifted to the launch photos page where I saw this aircraft. I did not find a caption, and a quick reverse image search in google did not return any helpful results.

I am fairly confident that it is not a "spaceplane".
What is this NASA UAV, and what is its function?

This is a Northrop Grumman RQ-4 Global Hawk. NASA has done some research on civilian applications for drones and this one appears to be for storm research. You can find more info on the project here.

Thanks! fyi I've just asked How did Northrop Grumman propose to make the Global Hawk nuclear powered?


text:
Am I seeing double? What kind of helicopter is this, and how many blades does it actually have?
This June 9, 2024 CNN news video begins with an inset of video of what looks like an Israeli IDF "event". Looking down from a relatively static point in the air, another helicopter is seen and there is movement on the ground. It might be thermal infrared (the image is monochrome, the ground is white and the moving objects are black), then again it might not be. I don't see any evidence of a hot engine like I do in other footage after 00:30.
What's striking, or at least distracting, is the appearance of parallel blades. I've seen rolling shutter effects cause straight blades of propellors to appear curved, but I haven't seen an effect that can double them, at least yet.
Is there any chance there are two rotors and we're looking from an angle? Or does this helicopter have only one set of blades and this is some kind of photographic effect? Maybe it's not thermal infrared, and it's a shadow on the ground?
I'm stumped.

It might be a composition of two frames or just the shadow

@sophit both of those possibilities are already essentially covered in the question.

I vote "shadow."

I'm just seeing shadow on the ground.

I vote @MichaelHall: the CH-53 is on the ground with people approaching from the back

@MichaelHall well it's night here and I left my helicopter blade-shaped board back in the US, so it's easier for me to do the math. I guess if they are say 15 cm wide and 2.5 meters above the ground, ya, it would be hard to tell. I'm slowly getting convinced. Since it's late and I won't be able to babysit the question for much longer, I'm deleting most of my comments. I guess it's ajust a really big helicopter!

@MichaelHall Oh, those blades would be roughly 50 cm wide, and it potentially "seats" 50. OK I am getting the picture. Now about that ghost-like faint tail shadow... Aha! The moon landings were faked! (humor)

now wondering if it was one CH-53K (which it's not), would the canted tailrotor cast distinct shadows of each individual tail rotor blade

@user721108, depends on sun angle, right?  I can make out a blurry tail rotor shadow, but it is mostly side-on.  And if you know what kind of helicopter it is not, what do you think it is?

It appears to be a greatly zoomed in overhead view of some variant of the CH-53.  (I haven't verified, but per another member, it's a S-65C-3 Export version of the CH-53D for the Israeli Air Force)
It is parked on the ground with people approaching the rear cargo entrance.  The extra blades you see are simply shadows.
Evidence they are shadows is that the tips of the blades and their shadows are aligned with the sun angle.  Double blades would be symmetrical radially.
Note too that the blade at 5:30 appears to cast almost no shadow because it is aligned with the sun and camera angle, making it look elongated rather than double.
Note:  The image below is reversed, but gives some idea of shape and scale of the CH-53.  (A still from the YouTube channel of "The Daily Aviation")

The brightness of the sun and its angle to the camera will play a big role in whether the actual blades appear dark like the shadow on the ground, (giving an appearance of double blades) or whether they will reflect more light back and appear lighter.
For example, consider the following photo of an SH-60 on the ramp at NAS North Island taken from Google earth where the shadows are distinct and dark, while the blades are very light colored.

I'd suggest that a loitering UAV (which they'd certainly want overhead to monitor everything going on, in any case) is a far more likely source of the images than a satellite. But otherwise, I entirely agree with the answer.

3 windscreens, SH-60 right  The CH-53 in the question must be a D version, or better an: "S-65C-3
Export version of the CH-53D for the Israeli Air Force."

@MichaelHall then I'll just say "Thanks for your answer! These images really helped me understand what's going on."

@sophit, im really not that good, i just had the advantage of knowing where i got the photo!  ;) NAS North Island

There's a lot of copy-paste in that video still - even the "23" aircraft is duplicated, as well as most of the figures.  I hope that's not being presented as journalism...

This is the NAS North Island source for the last photo:   https://www.google.com/maps/@32.7045016,-117.2090529,232m/data=!3m1!1e3?entry=ttu   Plenty to choose from.

Most of what's presented as "journalism" these days, @TobySpeight, is thinly veiled propaganda. Applies to all media from all sources. Everyone is pushing an agenda. The only difference is whether one happens to agree with the agenda being pushed by a particular source.


text:
Identify this commercial(?) jet approaching Songshan airport in Taipei with what looks like very long inner flaps
Taken from a bus window on a highway leaving Taipei going west and south, these photos show what I assume is a commercial jet on roughly northeast(?) approach to Taipei's Songshan Airport July 24, 2023 at 16:45 UTC+08 (local time).
Twin engines at the rear just in front of the tail, and sort-of-delta-ish-wings rather than skinny ones, but maybe it's just very long inner flaps compared to what I'm used to seeing? If so, maybe a short description of why the wings + flaps seem to look different than what a long time passenger might think flaps normally look like would be helpful.
Photos taken by cell phone through a tinted bus window pointing very high (almost straight up) by the third and closest one.

   click for full size

It could be a Bombardier Global 7500 by a quick search. I can't find any good pictures from under but they look kinda similar, and depending on the livery of the plane you saw, could've operated in Taiwan as a private jet

Wing shape a better match IMO than an MD-80 in the other answer. Also the winglets, almost visible in the source image.

This was just a quick search, I'm not a civilian aviation kind of guy. That's why I used an F/A-18 on my profile picture rather than, say, a 777

The pointy nose is also a better match. This could very well be it.

The gear placement is very similar too, although I couldn't find an image for the underside

It seems's you've nailed it, thank you for your speedy answer!

It was a Bombardier Global 7500 (all credits should go to Mateo, he was the first to identify the aircraft type correctly). This aircraft, registration 9H-VID was operating for VistaJet, flight VJT750 from Tokyo  (HND) to Taipei (TSA).

source: Jetphotos, copyright atc1110
A screenshot from the Flight Radar 24 replay, showing the flight ID is below:

Nice - traveling east out of Taipei on Freeway 1 even explains why I saw it high out the left side window of my "luxury" bus, and that Bombardier marketing focused on ultra-high-net-worth individuals and the Global 7500 is the largest, longest range, roomiest and most luxurious purpose-built business aircraft yet built explains why it's unfamiliar to me :-)

@uhoh apparently ultra-high-net-worth individuals like the smell of old cigarettes and of dogs
https://aviapages.com/aircraft/9h-vid/
(yes, I am sure they circulate ozone through the cabin after each use to deeply clean it, but still ... )


text:
Why are even drone flights prohibited due to the earthquakes near Mt Keilir, Iceland?
A "swarm" of over 20,000 earthquakes has rocked Iceland in the past 10 days — and it could spark a volcanic eruption links to this tweet by Almannavarnadeild ríkislögreglustjóra; The National Commissioner Of The Icelandic Police, Department of Civil Protection and Emergency Management:

Earlier today a tremor pulse was detected south of Mt Keilir, in the Reykjanes Peninsula, SW Iceland. No eruption has yet been detected but due to risks related to volcanic activity, all traffic near Keilir and Mt Fagradalsfjall is prohibited, including drone flights.

I can certainly understand large craft and especially those containing people, but why might Civil Protection and Emergency Management prohibit even drones that could be used to obtain scientific data on Mt. Keilir including changes in the mountain's appearance which might indicate an eruption was imminent?

Source

Most likely they are conducting low altitude air operations in the area and don't want to risk running a helicopter into somebody's sight-seeing drone.

@RonBeyer I see, so perhaps "all traffic... is prohibited, including drone flights." has exceptions which know who they are?

Maybe they don't want drone hobbyists to go near the volcano due to the high risk of eruption?


text:
How dangerous (or not) are some synthetic types of aviation hydraulic fluids based on organophosphates?
Insider's January 13, 2023 Gerard Butler says he mistakenly rubbed acid all over his face while filming 'Plane' and didn't realize until he was 'burning alive' links to the Late Night with Seth Meyers January 12, 2023 Gerard Butler Burned His Face with Phosphoric Acid While Filming Plane where after 06:16 Butler describes a scene where he's working on the wheels of the aircraft:

It's burning my face, and I mean burning. It turns out this is essentially phosphoric acid. And the airline pilots that were there watching go, "No!" They're trying to put water on my face. "Don't put water. It will make it worse!" And I'm just, like, burning alive. So it was intense.

The insider article also links to Spartan.edu's Facts You Should Know About Aviation Hydraulics and Landing Gear which under the Types of Hydraulic Fluid heading it says:

Synthetic Based Fluids: This type of oil is usually dyed purple and is typically composed of a man-made phosphate ester, an ester derived from an alcohol and phosphoric acid. However, it can also be colored either green or amber. Despite its benefits, it can ruin paints, soften some plastics, and sometimes slowly chip away at the insulation, which can degrade the wiring over time. This type of fluid is common on larger transport aircraft.

Searching Wikipedia for "phosphate ester" returns the Organophosphate article, which explains this is a large group of compounds with uses including pesticides, nerve agents and flame retardants.
So while the hydraulic fluid he got on his face likely did not contain phosphoric acid it still sounds like scary stuff.
Question: How dangerous (or not) are some synthetic types of aviation hydraulic fluids based on organophosphates?

https://avherald.com/h?article=4b6eb830  Makes scary reading.  The industry and regulators seem determined to ingnore the many bleed-air contamination events.

The most common fluids are Skydrol and Hyjet. Suggest searching for Hydrol MSDS and Hyjet MSDS. The MSDS will give you the answers you seek.

@DaveGremlin Holy hell! That makes me a little afraid to fly on anything but B787 now! Sure sounds like everyone's trying to sweep this under the rug.

Phosphoric acid isn't scary at all. It's added to all kinds of soda. Orthophosphates were the cause of the Flint water crisis: they stopped adding it to drinking water, causing corrosion and lead poisoning.

Here is the MSDS for Skydrol 500B-4, a phosphate ester-based hydraulic fluid. Seems pretty tame, as chemicals go. Example line, of a test putting the fluid on a rabbit to see if it irritates it:

Species: rabbit
Exposure time: 24 h
Assessment: not classified as hazardous
Result: no skin irritation

The hazard diamond gives it a health rating of "0" meaning non-hazardous. It's listed as a possible carcinogen, but there's so many things listed as possible carcinogens that's practically meaningless at this point.
All in all, pretty tame stuff and not likely to "burn someone alive!" Glancing through some MSDS for similar chemicals I don't see any huge red flags. Maybe he's allergic to the stuff?

Referring to the AVH article in comments.
The article is sensational associating several source and building a story form excerpts. However it misses facts and references to actual expert analysis, and it fails to explain what can be derived from all known elements, and what cannot.
This is what this study (named FACTS) actually does, for me with all appearances of scientific rigor. This report also mentions other past studies, showing this topic is not, like suggested in comments, hidden under the carpet. Furthermore, it list (in a long list) actions that now need to be done to move further, both for the regulators, the manufacturers and the operators.
When I mentioned this study in a comment, I was invited by the OP to post a summary, but note I'm not an expert in anything mentioned here, and I cannot evaluate whether the study was meaningful or not. Still I can read a report and select some excerpts which I hope are interesting for readers here. It's a 151-page report, so I'm not exhaustive, thou this post is a long one, and I possibly made some errors in assessing the relevance. I'm posting this as a community wiki, so everyone can add their own value. My suggestion is to read this report along with the AVH article and compare.
The context of the new FACTS study
My understanding is the study covers what is usually discussed as fumes in cabin and flight deck, and attributed to organophosphates pyrolyse in engine after a leak of lubricant. So it encompasses what the Aviation Herald displays in their article.

The quality of the air [...] on board commercial transport aeroplanes has been the subject of ongoing discussion for the past 60 years. The discussion has centred on questions concerning the possible health effects (acute or delayed) of specific cabin air contamination (CAC) events or of chronic exposure to repeated low levels of contaminants.

[Past] in-service measurement campaigns did not reveal exposure to concentrations of substances that could explain above mentioned concerns with traditional risk assessment. DG Move designed a research project [...] novel insights into the causes and possible toxicological effects of contaminants in particular during so-called smell in cabin (fume) events.

The objective of the FACTS project was based on an innovative approach [...], test flights, ground tests, experiments in stationary equipment and desk studies were performed.

TCP presence in fumes, past studies
Some of the past tests consisted in burning jet oil to create fumes.

[A study] by EASA was conducted between 2015 and 2017 by a consortium of the Netherlands
Organisation for Applied Scientific Research (TNO) and the Dutch National Institute for Public Health and the Environment (RIVM).3 This study characterised the chemical composition of turbine-engine oils (including pyrolysis breakdown products) in transport aircraft, and the toxic effects of the chemical.

It wasn't possible to detect any abnormal level of TCPs (tricresyl phosphates), the family of organophosphates suspected by crew members and general public to cause neurological problems when fumes fill the pressurized vessel.

The analyses detected 176 different chemical compounds in pyrolysed jet oil, as well as the presence of neuroactive products. The concentrations in the presence of an intact lung barrier are considered too low to be of major concern for neuronal function. Although TCP was present in the oils analysed, no ortho-isomers could be detected.

Some tests were done in-situ, both in aircraft with bleed air and electrical compressor (no bleed air), a total of 69 flights.

[A study] was conducted by a consortium of Fraunhofer ITEM and the Hannover Medical School. The study was based on a total of 69 measurement flights performed between July
2015 and June 2016 on eight types of aircraft/engine configurations. Of these flights, 61 were on aircraft equipped with engine bleed air systems, and the other eight were on Boeing 787 aircraft, which are equipped with electrical compressors (i.e. a ‘bleed-free’ system).

For all flights, measurement equipment was installed in the cockpit and in the cabin. Special attention was paid to organophosphates, particularly tricresyl phosphates (TCPs).

The result was negative again, cabin air quality is not different from air in offices which already contains TCPs and, counterintuitively, air in Boeing 787 isn't better.

The results indicate that the quality of cabin/cockpit air is comparable to the air quality observed in normal indoor environments (offices, schools, kindergartens, dwellings). The study also revealed that cabins supplied with electrical compressors were not devoid of TCP, which was detected on Boeing 787 aircraft at similar concentrations compared to aircraft with bleed supply.

None of the observations revealed instances in which occupational exposure limits and indoor guidelines were exceeded. No detected contamination reached critical or unusual concentrations for indoor environments.

The new study (FACTS)
The study first observed there was not enough data for any decision, except to collect more data, focusing on some compounds. From this standpoint the study is a great value, it identifies what is missing to get some valid conclusion (sections "gap analysis" for each task/test).

According to the studies that have been conducted to date, although many measurements have been performed in aircraft, there aren’t many measurements of contaminants, during events, when smell in cabin was reported.

This hampers the evaluation of consequences for maintenance procedures, the health of aircraft crew and passengers, and the implementation of mitigating measures if necessary. In the future, monitoring the air on board aircraft for a few dedicated marker compounds would constitute a major advancement in tracking the performance of air supply systems on board over time.

As described in this report, the research was conducted between 2017 and 2019 by a consortium consisting of TNO (coordinator), Fraunhofer, VITO, AIRBUS, Honeywell and RIVM, in collaboration with subcontractors and aircraft companies.

The study was facing a real challenge as fumes events are rare:

A multitude of research projects around the world have suggested that fume events may happen in about one of every 5,000 flights, although categorization of the events is extremely difficult. An extensive commercial flight campaign aimed at capturing fume events would thus be quite inefficient in terms of both cost and time, and it would not necessarily yield the desired outcomes. Even if such a campaign were to be able to capture sufficient data, the interpretation of the results would always be subject to doubt.

They decided to use a fumes simulator (BACS), to verify the results during test flights and to evaluate neurotoxicity on mice (and zebrafish for whole-organism reaction):

The BACS laboratory setup simulates the thermodynamic process acting on a contaminant, in order to assess influence of generic temperature and pressure conditions on compound decomposition. The BACS is capable of simulating air compression in engines and APUs, and it allows the simulation of targeted contamination ingestion, thereby yielding a full characterisation of the air following contaminant ingestion at the compressor exit and the ECS pack exit, respectively.

However, the BACS couldn't be used within the timeframe of the study, the report indicates it is currently used at "national level" to test engine oil, hydraulic oil and de-icing liquid, and it could be used on additional studies.
For the test flights, two experiments were conducted, on various phases (taxi-out, climb, cruise 45/60 minutes to FL420, descent):

Generate normal concentrations of contaminants during the baseline flight. Generate the highest possible concentration of contaminants during the test flight.

Details are pages 29 and next, sensors used are pages 34 and next. Detailed results are available, e.g. for TF1 on pages 46 and next. For those actually interested it's possible to get details like:

The highest concentration of organophosphates was measured for TBP, which increases in the cockpit from 3.36 μg/m³ at baseline to 12.4 μg/m³ during the ground-test event.

Some experiments were also conducted on the ground:

Various types of engine oils and hydraulic fluids were heated under laboratory conditions for chemical analysis and for predicting their toxicity according to various bioassays. The engine oils and hydraulic fluids that were used are representative of those most commonly used in aviation, along with one TCP-free engine oil.

The results of the new study
Some reports are public, some are confidential (see page 19). For TCP levels during test flights:

Residues were sampled by swiping the ECS parts (details page 110). E.g for 1/2/3-cresyl phosphates:

Results of organophosphate concentrations in deposits on the internal surfaces of ECS parts. No mono, di and tri ortho-cresyl phosphates were measured above the detection limit of 0.00001 µg/cm2. In all ECS parts, m/p isomers of tricresyl phosphate were identified. The total concentration of m/p TCPs ranged from 0.00001 to 0.02072 µg/cm2. In addition to the m/p isomers of TCP, 7–13 individual OPCs were frequently found in all ECS parts.

Test flights and residues shows more data are needed, and further studies must be conducted (see page 120).
For samples used for toxicity tests on mice and zebrafish:

Engine oils and hydraulic fluids were nebulised by pre-heated (90oC) air into a heated mixing chamber (90oC) with a spray nozzle. The spray nozzle was also preheated to 90oC, in order to decrease the viscosity and surface tension of the oil/fluid, thereby decreasing the droplet size. The oil/fluid was metred to the spray nozzle using an adjustable motor-driven syringe. The oil/fluid aerosol flow then entered the oven for pyrolisation. Pre-heated air was mixed with the aerosol at the entrance to the oven. The system was kept under pressure using a critical orifice downstream of the oven, along with a back-pressure regulator. After expansion, the fumes/aerosol were ready for sampling.

Results, details pages 124 and next:

Based on this finding, there is no need to adjust existing reference values for application to the cabin environment.

Only if exposure to a given chemical in cabin air approaches the reference value should additional attention be paid to the influence of longer exposure over 24 hours during the brief periods that are likely to occur several times a month. In general, reference values for the general public are lower than occupational reference values.

The study also recommends digging further in this area. It also proposes to improve the certification of ECS (and periodic verifications) and the integration of specific sensors, and also notes:

Given the variety of aircraft standards and their adoption by the various aviation authorities, it seems necessary to harmonise the certification process for bleed air quality across authorities (primarily FAA and the EASA) and to enforce the respective requirements consistently in the engine-certification process.

In the overall conclusions, the study acknowledge the current lack of data, and the limited significance of the tests conducted. This seems to me a honest position, neither trying to hide, nor to reassure, just saying that based on measurements, nothing can be said dangerous, but measurements are likely insufficient to be conclusive, and a lot of work has to be done to clarify the situation, e.g.:

A complete understanding is lacking with regard to processes that influence chemical emissions throughout the air-supply system as a whole, starting from the LP and HP sections, through the ECS packs and ducts, to the cockpit/cabin.

It is unclear which components might be formed along the route from the source to the flight deck and passenger cabin.

Few measurements campaigns have been conducted to study de-icing, despite the serious
contaminant effects that the spraying of de-icing agents can have on CAQ. Although many
cases of glycols entering the cabin have been reported, little data has been collected on this phenomenon.

If the hydraulic fluid is pressurized at 3000 psi, and the pressure is released in an uncontrolled way, it is very dangerous to anything in the way.

I think that the question's wording: How dangerous (or not) are some synthetic types of aviation hydraulic fluids based on organophosphates? makes it clear that I'm asking about a differential danger associated with the composition. As currently written, this is basically "Older model Steinway upright pianos are dangerous, because if someone drops one on you..." answer.


text:
Are there any statistics of parachute deployment from gliders?
Thinking about this question, I realised that I've only worn a parachute inside an aircraft when flying sailplanes.  I wondered how often and how successful are glider bail-outs- have the numbers been collected anywhere?
I'm mainly asking about sailplanes that the pilot (and passenger) need to climb out of,  rather than paragliders and hang gliders - reserves seem to be deployed fairly frequently in those cases.

You should be able to collect some data by sampling NTSB events for some period, say a decade's worth, of glider mid airs and structural failures.


text:
Does the EASA/FAA require additional life vests, and life vests for infants/children?
Is there some requirements (EASA or FAA) for additional life vests, and life vests for infants/children on-board estimation?

Welcome to aviation.SE! This question might be helpful.

I'm only familiar with FAA regulations so I'll answer based on my knowledge of them.
For Part 121 operations (most commercial airlines), Section 121.339 of the FARs simply states the following:

(a) Except where the Administrator, by amending the operations specifications of the certificate holder, requires the carriage of all or any specific items of the equipment listed below for any overwater operation, or upon application of the certificate holder, the Administrator allows deviation for a particular extended overwater operation, no person may operate an airplane in extended overwater operations without having on the airplane the following equipment:
(1) A life preserver equipped with an approved survivor locator light, for each occupant of the airplane.

Therefore based on an interpretation of the regulations, there must be enough life preservers on board for all occupants of the aircraft, including children. I would assume therefore that airlines would always make sure to have enough and probably a few extras to meet this requirement. Given there are only a set number of seats per aircraft, airlines should have no problem doing this even taking into account children. You can only have so many occupants for a given flight.

as example, it could be any additional life vests on board. So, during SAFA ramp inspection will it be classified as a non-compliance finding?

From EASA Air-ops

NCC.IDE.A.220 Flight over water
(a) The following aeroplanes shall be equipped with a life-jacket for each person on board
or equivalent individual floatation device for each person on board younger than
24 months, stowed in a position that is readily accessible from the seat or berth of the
person for whose use it is provided:

https://www.easa.europa.eu/system/files/dfu/Part-NCC%20IR.pdf
https://www.easa.europa.eu/system/files/dfu/Consolidated%20unofficial%20AMC%26GM_Annex%20VI%20Part-NCC.pdf

do you have a link to the original document as well?


text:
How do fighters detect laser locking?
I've been wondering this for a while. I understand how planes detect electromagnetic waves with it's radar but I don't get how they detect if missile has locked to the plane using laser. Only ways I can figure are some kind of tiny receptors all around the plane but it sounds very impractical way.

"Receptors all around the plane" is pretty much how regular radar warning systems work.

When someone shoot laser to your mouth you can still see the flash of laser. You don't need to put detectors everywhere, but only a few to detect scatters and diffraction. However, you might be right: a laser warning system won't work well for low-power beams unless the whole vehicle is covered by sensors (Most laser warning systems produced so far can not detect laser beam-riding missiles because of their weak emissions which have signals less than 1% of laser range finder power. https://dspace.lib.cranfield.ac.uk/handle/1826/1047)

@user3528438 Please post answers in answers, not in comments.

Unless you can provide more details, I think, in the system you are after, the laser beam is delivered by a designator (airborne or on the ground) but not from the missile itself. The beam is not a cylinder, it diverges by some angle (e.g. 10 milliradians). Therefore at a certain distance the beam diameter is several meters and only 3 or 4 sensors are necessary to detect it from any direction.

Which weapon includes laser guiding?

They have a number of cats positioned around the aircraft, best laser detection known.


text:
I want to become a commercial pilot, can you do that through the RAF?
I want to become a commercial pilot, can you do that through the RAF?

Being a military pilot is very different than just flying. A military service is to protect a country, by trading your life in combat if necessary. If your goal is to fly jets, look for airlines that recruit "pilots" with no flying experience.

Even though many of the airlines higher x RAF pilots?

Experience as a fighter pilot is sure makes a person a very good candidate, but it is by no means the only way. All I am saying is that serving a military has its own life style, and you have to be prepared to sacrifice a lot in personal life.

@kevin Most air force pilots are not fighter pilots.  A C17 or A440 pilot, for example, will be a natural fit.

@DanielMurphy Another way to look at it is that an RAF pilot will almost certainly make a good commercial pilot, so it stands to reason that many ex-RAF pilots go on to fly commercially. However, the reverse doesn't stand true - a good commercial pilot won't necessarily make a good RAF pilot. Joining the military on the strength of a civilian career in 5 - 10+ years is probably a bad move. You'd probably be shocked at how little (relatively speaking) flying your average RAF pilot does day to day compared to a commercial operator clocking up hours

Yes, you can. It means giving a commitment for a fair number of years in service of your country, where you will be trained as a pilot (assuming you get on to that - there are more jobs in the RAF than just pilot!). After your service, one thing you can do with your military flying experience is become a commercial pilot.
When I was young enough to consider it, there were 3 ways to become a commercial pilot

Learn in the airforce
Pay your own way (PPL, CPL, ATPL etc)
Get a scholarship from a big carrier like BA. There were usually about 4-6 given per year to the highest achievers.

When I spoke to someone at the RAF they told me I could not become a commercial pilot through them. What is the process from the time you leave the RAF? or can you do a aviation science degree while in your service?

Just to be clear, I believe that, like in the US, that the hours you earn in the service can be applied towards a type rating or license. You would still have to pass the knowledge and skills tests before being issued a license. Militaries do not issue private/commercial/ATP licenses, a military pilots license is not the same as a civilian one.

All they mean is that the RAF will not provide you with a commercial pilots license since they have no need for it.  But training for and flying multi-engine transports, for example, will give you at least as good a training as the civilian route - some would argue better.

And what way did you choose?

@avtomaton A career in financial technology. My eyesight was not good enough for the airforce, and my pockets were not deep enough to do it myself. Alas, a PPL is the best Ive got so far.

Well I'm pretty confident going through Uni as it would be quicker and I can become a flying instructor after I finish the degree!

@DanielMurphy I would look very hard at what you earn as a flight instructor and how long it will take you to go from CPL/CFI to ATPL. Some instructors spend 3-4 years instructing to get up to ATPL and earn minimum wage (in the US). I know a very successful instructor who owns his own school that makes only about $14k from instructing per year. Newly minted ATPL pilots make between $30k and $40k per year. It takes 10-15 years to get up to a respectable wage.

If you were to serve in the RAF as a pilot (no matter the appointment e.g. rotary, fast jet, or multi engine) after your service you can become a commercial pilot with additional training for around 6 months which is very cheap.
Also it will help you get a good quality job as a commercial pilot as you have officer training & loads of flight hours & (if chosen) part time instructor in the Grob Tutor/115e as well.


text:
Do coaxial rotors provide twice the amount of lift?
Do coaxial rotors provide twice the amount of lift given same diameter and RPM?

Related: Why does the Ka-50 (Hokum) have two main rotors, one on top of another?

Possible duplicate of What is the purpose of having contra-rotating props on an aircraft?. Although this is a question about rotorcraft, I'd say the question is basically the same: the propellers are just pointing in a different direction. But if there's a significant difference I'm happy to retract.

Yes they can give twice the amount of lift if blade angle of attack is a variable, but require more power to do so. Momentum theory predicts:

a 28% power penalty on this configuration, when compared to running the two rotors in isolation, when the two rotors are operated at equal thrust.
a 22% power penalty when the two rotors are operated at equal rotor torque.
a 41% power penalty when the rotors have no vertical separation.

Experiments have shown a power penalty that is less than predicted by momentum theory: 16%.
Source: Principles of Helicopter Aerodynamics, J. Gordon Leishman, section 2.15.1


text:
In what way(s) will making an airplane electric help to make it "quiet"?
In this blog I read about the Quiet Flight Initiative, which - if I understand correctly - will be quieter than a comparable carbon fueled plane at least in part because it is electric. It's an engineering challenge associated with Embry-Riddle Aeronautical University.
What aspects of the plane design - when switching from combustion engine to electric motor - will help reduce noise? I had thought that most external aircraft noise heard on the ground (in this case, National Parks) is associated with the propellor, and so noise is closely linked to performance, not the particular method of torque generation.

@ymb1 Considering that batteries are roughly 50 to 100X heavier than fuel for an equivalent amount of useful work, it may be tough to do that. I don't see why it being electric would make that easier, except perhaps re-start reliability.

@ymb1 I see! I noticed for electric power: "Greatly reduced noise, allowing take-off from locations where other powered aircraft are not permitted" also says "[citation needed]" but it looks like there may indeed be an answer there. But I still don't understand why the electrification reduces noise there either - doesn't it come from the propellors?

You are right, propeller noise is dominant in case of GA aircraft, but not all propellers make the same noise. Much depends on blade loading and tip speed - making the propeller larger and letting it turn more slowly will improve efficiency and reduce noise. This has worked very convincingly for model aircraft over the last 30 years. GA engines are normally ungeared, so their propeller speed and diameter are the same. Switching to a geared IC engine like a Rotax 914 not only makes the engine lighter but also the propeller less noisy. Switching to an electric motor, which can produce high torque at low speed, will allow to exploit this effect to the fullest.
Other sources of noise will profit from electrification, too. The exhaust noise will be completely avoided, and airframe vibrations will be greatly reduced. Radiator noise will fall away, too. It is a small source of noise, but every bit counts.
What will be left is the noise of the slower propeller(s) and aerodynamic noise. Now landing gear retraction would be the next big step in noise reduction.


text:
At what altitude might a pilot be able to see at least the brightest stars during the day?
In this comment I pondered if I should ask:

"Did Test pilot and astronaut Joseph A. Walker see stars during the day when flying the X-15 above the Karman line?

But instead, I'll just ask at what altitude might a pilot be able to see at least the brightest stars during the day?
Assume cockpit lights and panel illumination are dim-able and a high tech high altitude aircraft (e.g. the X-15 or something modern or near-future) is used.
I don't think it's easy to see bright stars during the day at cruise altitude by eye without some help, but at some altitude it should be.
Is there any information on what altitude this might be?

Venus is visible from the ground during the day if you know exactly where to look. You might have to be more specific about which stars, and how "visible" they have to be to qualify.

@Dave-CFII it's difficult to pre-specify without being in danger of excluding an otherwise helpful answer. I'm guessing that commercial pilots don't regularly see stars during the day, and while a cardboard tube and some google can help people see Venus during the day, it wouldn't count as a star. Unfortunately the Sun does count; hopefully nobody will post that as an answer.

If you don't get a good answer here, you could try astronomy.SE

I see a very bright star every day during the day with naked eye at altitude 0 :-)

SR-71 pilots saw the stars, but of course there is no account of the exact height, they started to see them. They were flying around at 80000 feet at some point in their mission profile. Basically you have to get above most of the atmosphere. So you should start to see stars above 43000 feet. Of course there are some other options, you see them during an eclipse or above the Arctic circles in the right season. You can always see the stars, if you know where to look and if you have a telescope, but I presume you mean to see them with the naked eye?

I've not heard any reports of seeing stars during the day from Concorde at 60,000ft, so that narrows it down a bit.

Well the height of the troposphere varies with season and latitude. Also the concorde has very small windows. I should also say that this is a guesstimate. The troposphere scatters most of the light or rather the water vapor.

@bogl perhaps mike was typing on a telephone at the time

Yes! Telescope! Although I can see at least one star on my telephone too!

@mike hehe, not being rude/serious or anything but are jokes allowed in comments?, cause I have one on my mind on another answer and it’s really good.

Venus (not a star, but often mentioned in this context), Arcturus, Vega, Rigel, Sirius, and several other very bright stars are visible in daylight from sea level when sky conditions are right -- if you know exactly where to look.
Random stars are reportedly visible from within a deep enough hole (a well or mine shaft, for instance), because the bright scattered light of the general sky is mostly blocked by earth or rock and the eyes are adapted to the dimmer light.
So, to answer the question, in the limit, below ground level (though you're unlikely to fly there), or at sea level under the right conditions.

Yes, but the thing with the hole is a hoax, that doesn't work. What does work are binoculars.

Tell it to Aristotle and Sir John Herschel (see edit above).

The link does not confirm the ability to see stars from the bottom of a shaft, but rather refutes it.

Since they failed, even with binoculars, one wonders if sky conditions were less than optimal (a cirrus layer that isn't even readily visible would broaden the point of a star enough to make it invisible against the general scatter).  Star visibility from the ground in daylight is well documented and repeatable, and doesn't require visual aids, if only the sky is completely clear.

@ZeissIkon I've just asked Can an average person see stars from the bottom of a well or through cardboard tubes? Definitive answer required!


text:
Who put a model of the Space Shuttle at the Portal of the Folded Wings Shrine to Aviation in Los Angeles Ca?
Background
This answer to Help identifying this landmark and road in "Los Angeles 1940s, Residential Area in color" in Travel SE identified the structure as the:

Portal of the Folded Wings Shrine to Aviation:

The Portal of the Folded Wings Shrine to Aviation is in Los Angeles, California. The shrine is a 75-foot-tall (23 m) structure of marble, mosaic, and sculpted figures and is the burial site for fifteen pioneers of aviation. Designed by Kenneth A. MacDonald Jr. and sculptor, Federico Augustino Giorgi, it was built in 1924 as the entrance to Pierce Brothers Valhalla Memorial Park Cemetery

From the linked question:

The NASS video Los Angeles 1940s, Residential Area in color [60fps, Remastered] w/added sound is a processed version of this archived footage.
Starting at about 02:18 a movie camera points backwards from a vehicle driving down a road, pointed at the car behind but also showing few buildings and mountains in the background.
However on the left there is a large, notable building...

Screenshots from the video (click for larger):

Question
Looking in Google maps there's an image that seems to be dated March 2022 https://goo.gl/maps/9igZNqgoJDqxENNS7 that shows a model of the Space Shuttle in front of the monument.
I'm curious who donated and/or build the model and since this is in a mortuary, if there is a commemoration to astronauts who lost their lives flying the Shuttle or in spaceflight in general.
There must be an interesting story here.

It appears the trustees of Valhalla Memorial Park had it placed in 2007 as a memorial to the crews lost in the Challenger and Columbia mishaps.
There's a good summary at Roadside America which states:

In 2007 the Portal was joined by a more modern, just as impressive,
companion: a 21-foot-long model of the Space Shuttle (It's big, but
not as big as the real thing, which is 122 feet long). Mounted atop
some poles, nose up, landing gear down (you can spin the rubber
tires), it's positioned as if it's about to land in the cemetery --
because it's a memorial to the crews of the doomed Space Shuttles
Challenger and Columbia. The insignia for Columbia is painted on its
left side, the Challenger on its right. Plaques in the lawn directly
below the insignia portray the seven astronauts who perished in their
respective spacecraft. The crewmembers aren't buried with the other
aviation stars at the Portal, but the Shuttle model serves as their
cenotaph.
In keeping with the Rotunda's theme of rebirth, the Space Shuttle
memorial is also an example of creative recycling. It is, in fact, a
former Hollywood movie prop, used in the ridiculous 2003 sci-fi
disaster film The Core, where it played the Space Shuttle Endeavour.


text:
Can drone with two propellers above one another fly vertically upward without spinning?
Basically, like the propellers setup in this image without the tail end bit:

Where the propellers will be spinning in opposite directions. This would, in theory, counteract the angular momentum to a degree right? So would this be able to fly vertically upwards without spinning?

Welcome! The answer is yes. Seems to be a duplicate of Why does the Ka-50 (Hokum) have two main rotors, one on top of another? or How can a helicopter be designed without a tail rotor?

That rear propeller does not keep the helicopter from spinning, it helps tilt the vertical lift component into a horizontal one, meaning forward and backward motion.

The rear propeller on that model is needed only because it is cheap one without cyclic controls.  Better coaxial R/C helicopters have cyclic control and so don't need anything on the tail to fly in any direction (though they are usually designed for extreme self-righting stability, so can't pitch to fly very fast, unlike full-scale coaxials which are not, and which can fly at useful speeds.

Yes, because spinning in the opposite direction produces counterbalancing torque. Those rotor over rotor models adjust yaw by small variations in the speed of the rotors, so that one produces a bit more torque than another.
There are a number of large helicopters that use two main rotors to the same effect, such as the CH47 Chinook (front and rear) and the Kamov KA31 which uses the same rotor over rotor configuration as the model you picture.

I don't know about drones and toys, but co-axial rotor helicopters such as the Kamov Ka-31 and Ka-115 do not adjust yaw by varying the relative speeds of the rotors. The rotors are geared together and remain synchronized. It is the relative drag of the rotors that must be adjusted, which is easily managed via a separate swash plate for each rotor.

Varying rotor speeds is indeed how it's usually done on simpler RC models because having two motors is cheap at that scale and mechanically more sound - those models have a tendency to hit stuff, which would quickly damage the meshing. But good comment for the Kamov!

@SylvainBoisse, model rotors also have small angular momentum, so quickly accelerating them is possible. Full-scale rotors don't—moment of inertia scales with fifth power of diameter. So full-scale rotors can't be varied in speed with any useful precision.

The very inexpensive models have fixed pitch blades, so they can't adjust yaw by varying pitch - so they only adjust speed. True that the KA31 will do this by varying pitch instead, a more accurate method. I should have mentioned that...

The 'fly vertically upwards' is achieved simply by increasing the rate of both motors. They still counteract each-other's torque so no spinning but now, because each rotor is angled to provide upwards force despite counter-spinning, they both provide more lift and "up she goes...."